Display device with improved drive arrangement

ABSTRACT

A self-luminescence display device, in which dispersion in display among a plurality of pixels, caused by dispersion in characteristics among drive thin-film transistors, is decreased and uniform display free of unevenness can be obtained. The device includes a plurality of pixels having current drive type luminescent elements, and parallel-connected n (n≧2) thin-film transistors to feed a drive current to the respective current drive type luminescent elements. The transistors are arranged in different pixels, respectively, for example, in a first region of pixels adjacent to one another along a first direction. A second region of dummy pixels can be provided on at least one side of said first region along said first direction.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. application Ser. No. 10/304,700, filed Nov.27, 2002 (now U.S. Pat. No. 7,157,847). This application relates to andclaims priority from Japanese Patent Application No. 2001-363915, filedon Nov. 29, 2001. The entirety of the contents and subject matter of allof the above is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and, moreparticularly, to a structure of an active matrix type organicelectroluminescent display.

2. Description of the Related Art

Active matrix driven organic electroluminescent displays (referred belowto as AMOLED) is expected as flat panel displays of the next generationsucceeding conventional liquid crystal displays.

Conventionally, a two-transistor structured circuit, as disclosed inJP-A-2000-163014 (first prior technique), comprising a drive thin-filmtransistor (referred below to as EL drive TFT) for feeding current toorganic electroluminescent elements (referred below simply to as ELelement), a holding capacitor connected to a gate electrode of the ELdrive TFT for holding a picture signal voltage, and a switch thin-filmtransistor (referred below to as switch TFT) for feeding a picturesignal voltage to the holding capacitor, has been known as a fundamentalpixel circuit for a pixel drive circuit of AMOLED.

The two-transistor structured fundamental pixel circuit causes asignificant problem that nonuniformity in a picture is caused bydispersion every pixel in a threshold voltage (Vth) and mobility (μ) ofthe EL drive TFT due to dispersion every location in the crystallizingproperty of a semiconductor thin film (for which a polycrystal siliconfilm is ordinarily used) constituting the EL drive TFT.

Since dispersion in threshold voltage and mobility results in dispersionin a drive current value of the EL element, emission intensity dispersesto cause minute unevenness to be seen in representation.

Such unevenness in representation becomes particularly problematic whena drive current value is small to represent half tone.

Several measures have been devised in order to suppress thatnonuniformity in representation, which is caused by such dispersion inthe characteristics of an EL drive TFT.

For example, JP-A-11-219133 discloses a method, in which dispersion in adrive current value is suppressed by making channel length and channelwidth of an EL drive TFT fairly greater than an average crystal particlesize of polycrystal silicon constituting the EL drive TFT (referredbelow to as second prior technique).

Also, JP-A-2000-3305027 discloses a drive method by a so-calledpulse-width modulation, in which an EL drive TFT is driven as a binaryswitch for effecting a complete OFF state or a complete ON state andtone of a picture is represented by changing a duration of emission(referred below to as third prior technique).

Also, JP-A-11-73158 discloses an area tone system, in which a pluralityof EL elements having different luminescent areas are provided in a unitpixel, and an EL drive TFT is connected to each of the plurality of ELelements and driven as a binary switch for effecting a complete OFFstate or a complete ON state, whereby tone is represented by changingluminescent areas (referred below to as fourth prior technique).

Also, U.S. Pat. No. 6,229,506B1 discloses a method, in which four TFTSare provided in a pixel to constitute a circuit for canceling dispersionin a threshold voltage of an EL drive TFT whereby dispersion in drivecurrent is decreased (referred below to as fifth prior technique).

Also, JP-A-8-129359 discloses a method, in which a plurality of EL driveTFTs having different current drive capacities conformed to a pluralityof tone currents are connected in parallel to one EL element within eachpixel and driven as binary switches for effecting a complete OFF stateor a complete ON state, whereby tone representation is controlled bytone currents supplied from the plurality of EL drive TFTs (referredbelow to as sixth prior technique).

Also, JP-A-2000-221903 discloses a method, in which two EL drive TFTsare provided in a pixel to decrease dispersion in threshold voltages inthe EL drive TFTs, thereby reducing dispersion in drive current(referred below to as seventh prior technique).

However, the prior techniques described above involve the followingproblems.

The second prior technique is directed to averaging dispersion everylocation in the crystallizing property of the polycrystal silicon byincreasing TFT size. However, even when TFT size is increased, it cannotbe made greater than pixel pitch.

Accordingly, since a size of an EL drive TFT for driving an EL element,which constitutes each pixel, is limited within an area of a pixel, andthe crystallizing property of a polycrystal silicon film disperses everylocation, it is not possible to compensate for dispersion between thecharacteristics of an EL drive TFT in a particular pixel and thecharacteristics of an EL drive TFT in a pixel adjacent the particularpixel.

It is to be noted that what can be averaged by increasing a TFT size isonly dispersion in crystals sized within the TFT size.

Accordingly, it is difficult in the second prior technique to obtain afairly uniform property of representation.

For the effect of averaging picture representation with the third priortechnique, the pulse-width modulation driving is one of valid methods asan AMOLED driving method as having already been proved.

However, known as an essential problem in this driving method isbleeding in a picture generated when animation called pseudo-profile isrepresented because tone representation is made by luminescence pulse,which is developed on time base.

Also, because of a need for processing a short signal pulse conformed todigital tone, there is caused a problem that the drive circuit isincreased in operation frequency and power consumption.

Also, there is also caused a problem that a vertical scanning circuit;which may ordinarily be a simple circuit, becomes complex and a circuitarea is increased.

The fourth prior technique is much effective in uniformizing picturerepresentation, but multitone is difficult since it is necessary to formin a unit pixel EL elements having areas conformed to digital tone andto form EL drive TFTs corresponding to the respective EL elements.

Also, it has been known that EL elements are ordinarily decreased inluminescent areas together with operation duration.

In the case of using EL elements having different luminescent areas,deterioration is caused with time beginning with an EL element, whichhas a small area corresponding to a low-tone bit, thus causing also aproblem that normal tone becomes difficult with time.

With the fifth prior technique, the provision of a circuit for cancelingdispersion in threshold voltage of an EL drive TFT necessitates awiring, which is not necessary in a conventional two-transistorconfiguration, so that a decrease in numerical aperture and yield inmanufacture causes a problem.

Also, what can be cancelled is only dispersion in threshold voltage, anddispersion in mobility remains intact. Therefore, there is caused aproblem that no fairly uniformizing effect is obtained on drive current.

With the sixth prior technique, a plurality of EL drive TFTs havingcurrent drive capacities conformed to digital tone are connected inparallel.

However, it is apparent that normal tone representation is madedifficult when the plurality of EL drive TFTs disperse incharacteristics.

Also, since the plurality of EL drive TFTs are formed in a single pixelin this method, the technique is in no way effective in decreasingdispersion in representation among a plurality of pixels.

With the seventh prior technique, dispersion in drive current can bedecreased in the case where one of two EL drive TFTs connected inparallel is varied in characteristics, but dispersion in drive currentcannot be decreased in the case where both the two EL drive TFTs arevaried in characteristics, and besides the two EL drive TFTs are formedin a single pixel, so that the technique is in no way effective indecreasing dispersion in representation among a plurality of pixels.

SUMMARY OF THE INVENTION

The invention has been thought of in order to solve the problems of theabove prior art, and has its object to provide a technique for displaydevices, in which dispersion in representation among a plurality ofpixels, attributable to dispersion in characteristics of drive thin-filmtransistors is decreased and uniform representation free of unevennesscan be obtained.

Also, another object of the invention is to provide a technique capableof decreasing voltage drop and power consumption caused by resistance oftaken-out wirings of cathode electrodes in a display device.

The above and other objects and novel features of the invention will bemade apparent from the descriptions in the specification of thisapplication and the accompanying drawings.

An outline of a typical one of the inventions disclosed in thisapplication will be simply described below.

That is, the invention has a feature in that a plurality of EL driveTFTs are connected in parallel to current drive type luminescentelements arranged in respective pixel regions, current is supplied tothe current drive type luminescent elements from a plurality of currentsupply sources, and the plurality of EL drive TFTs are arranged in aplurality of pixel regions at intervals corresponding substantially topitch of pixel.

The plurality of EL drive TFTs are connected in parallel whereby it ispossible to average dispersion in drive current, attributable todispersion in threshold voltage and mobility among the plurality of ELdrive TFTS.

However, only making EL drive TFTs in plural and in parallel does notassure averaging dispersion in drive current for an EL drive TFTcorresponding to a particular pixel and, for example, pixels adjacent tothe particular pixel.

Nonuniformity in representation is caused by dispersion in drive currentfor EL drive TFTS in a plurality of pixels, which dispersion isattributable to dispersion in the crystallizing property of asemiconductor film constituting TFTs and spatial dispersion in filmynature of an insulating film.

Since EL drive TFTs are arranged regularly at the same intervals asarray pitch of pixels, it may be thought that dispersion in drivecurrent is attributable to dispersion in the crystallizing property of asemiconductor film and spatial dispersion in filmy nature of aninsulating film on a scale of array pitch of pixels.

In order to average such dispersion, it is effective to spatiallydisperse and arrange the plurality of EL drive TFTs at array pitch ofpixels.

Accordingly, a plurality of EL drive TFTs are connected in parallel tocurrent drive type luminescent elements arranged in respective pixelregions, current is supplied to the current drive type luminescentelements from a plurality of current supply sources, and the pluralityof EL drive TFTs are arranged in a plurality of pixel regions atintervals corresponding substantially to pitch of pixel, wherebydispersion in drive current supplied to the current drive typeluminescent elements corresponding to respective pixels can be decreasedand representation can be averaged.

The more the averaging effect by means of the plurality of EL drive TFTsdistributed and arranged spatially, the more the number of TFTsconnected in parallel.

It is theoretically predicted that the magnitude of dispersion in drivecurrent decreases inversely proportional to √N with an increase in Nwhen the number in parallel is N. Since pixels are limited in size, N=2to 12 is a practical value according to the rule of fine processingthin-film transistors (TFT) in the present circumstances.

Also, when the number of TFTs in a pixel is increased, it is difficultto ensure an area for EL elements, which contribute to emission oflight.

According to the invention, numerical aperture is enhanced by providinga reflective layer in a manner to cover at least a part of EL drive TFTsand forming current drive type luminescent elements on the reflectivelayer.

Also, since current from the luminescent elements in all pixels flowsthrough taken-out wirings of cathode electrodes of current drive typeluminescent elements arranged in respective pixel regions, it isimportant to decrease resistance of the taken-out wirings.

According to the invention, voltage drop and power consumption caused byresistance of taken-out wirings are minimized by shortening lengths ofthe taken-out wirings, which are connected electrically to cathodeelectrodes of a plurality of current drive type luminescent elements,extending from an external connection terminal to a contact area.

Concrete examples will be shown in the following embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a first embodiment of the invention;

FIG. 2 is a plan view showing a pixel arrangement in the display deviceaccording to the first embodiment of the invention;

FIG. 3 is a circuit diagram showing an entire display unit includingequivalent networks and a driving circuit in a matrix display section ofthe display device according to the first embodiment of the invention;

FIG. 4 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a second embodiment of the invention;

FIG. 5 is a plan view showing a pixel arrangement in the display deviceaccording to the second embodiment of the invention;

FIG. 6 is a circuit diagram showing an entire display unit includingequivalent networks and a driving circuit in a matrix display section ofthe display device according to the second embodiment of the invention;

FIG. 7 is a cross sectional view showing a cross-sectional structure cutalong the line X-X′ shown in FIG. 5;

FIG. 8 is a cross sectional view showing a cross-sectional structure cutalong the cut line Y-Y′ shown in FIG. 5;

FIG. 9 is a cross sectional view showing a cross-sectional structure cutalong the cut line Z-Z′ shown in FIG. 5;

FIG. 10 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a third embodiment of the invention;

FIG. 11 is a plan view showing a pixel arrangement in the display deviceaccording to the third embodiment of the invention;

FIG. 12 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a fourth embodiment of the invention;

FIG. 13 is a plan view showing a pixel arrangement in the display deviceaccording to the fourth embodiment of the invention;

FIG. 14 is a cross sectional view showing a cross-sectional structurecut along the line X-X′ shown in FIG. 13;

FIG. 15 is a graph indicating the relationship between the number N ofthin-film transistors for driving parallel organic electroluminescenceelements and dispersion in luminance among pixels;

FIG. 16 is a plan view showing an entire configuration of displaydevices according to the respective embodiments of the invention;

FIG. 17 is an exploded, perspective view showing an entire configurationof display devices according to the respective embodiments of theinvention;

FIG. 18 is a cross sectional view showing an essential part of across-sectional structure of display devices according to the respectiveembodiments of the invention;

FIG. 19 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 20 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 21 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 22 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of

FIG. 23 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 24 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 25 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention;

FIG. 26 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention; and

FIG. 27 is a view illustrating the manufacturing process of the displaydevice according to the second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments according to the invention will be described in detail withreference to the drawings.

In addition, the same numerals and letters denote elements having thesame functions in all the drawings, which illustrate embodiments, andrepeated explanations therefor are omitted.

First Embodiment

FIG. 1 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a first embodiment of the invention, andFIG. 2 is a plan view showing a pixel arrangement in the display deviceaccording to the first embodiment of the invention.

In a self-luminescence display device according to the invention,organic electroluminescent elements (referred simply below to as ELelements) of respective pixels are driven by three drive thin-filmtransistors (referred below to as EL drive TFT) provided on differentpixel regions.

In the first embodiment, respective EL drive TFTs are arranged in anassociated pixel, the next pixel on the right side and the further nextpixel but one on the right side.

In FIG. 1, there are shown three pixel regions surrounded by scanningsignal wiring electrodes (Gm, G(m+1)), picture signal wiring electrodes(Dn to D(n+1)), and anode current feeding wiring electrodes (A(n−1) toA(n+2)), which constitute a part of a TFT matrix.

A pixel in a row m and a column n is defined by a region surrounded byscanning signal wiring electrodes (Gm, G(m+1)), a picture signal wiringelectrodes Dn, and an anode current feeding wiring electrode An.

Formed in respective pixels are switch thin-film transistors (referredbelow to as switch TFT) (Qs(m, n)), three EL drive TFTS (Qd1(m, n),Qd2(m, n), Qd3(m, n)), and a charge-storage capacitance Cst(m, n).

An anode electrode of an EL element OLED(m, n) is connected to a drainelectrode of the EL drive TFT (Qd1(m, n)) via an EL connection wiringelectrode 15.

The EL element OLED(m, n) belonging to a pixel in row m and column n isconnected not only to the EL drive TFT (Qd1(m, n)) in the pixel but alsoin parallel to the EL drive TFT (Qd2(m, n+1)) formed in an adjacentpixel in row m and column (n+1) and the EL drive TFT (Qd3(m, n+2))formed in an pixel in row m and column (n+2) such that current is fedfrom three anode current feeding wiring electrodes (An, A(n+1), A(n+2)).

All gate wiring electrodes 14 of the three parallel-connected EL driveTFTs are connected to a drain electrode of a switch TFT (Qs(m,n)) of apixel in row m and column n via an EL connection wiring electrode 12.

Also, a charge-storage capacitance Cst (m, n+2) is formed between gateelectrode nodes of the three EL drive TFTs and the anode current feedingwiring electrode A(n+2) to be able to keep voltage of the gate wiringelectrodes 14 for a predetermined period of time.

In the embodiment, scanning signal wiring electrodes G are sequentiallyscanned, and a switch TFH (Qs), to which a scanning signal wiringelectrode G made at H level is connected, is made ON.

Thereby, a picture signal voltage is fed via the switch TFH (Qs) to acharge-storage capacitance Cst from the picture signal wiring electrodesDn to be held on the charge-storage capacitance Cst.

Based on the picture signal voltage held on the charge-storagecapacitance Cst, the respective EL drive TFTs (Qd1, Qd2, Qd3) feed tothe EL elements OLED current corresponding to the picture signal voltageheld on the charge-storage capacitance Cst during one frame.

Thereby, the EL elements OLED emit light to display a picture image.

In addition, with the embodiment, gate length, channel length, andchannel width are set so that current fed to the respective EL driveTFTs (Qd1, Qd2, Qd3) becomes substantially equal to a current fed by asingle EL drive TFT.

In the embodiment, the respective EL drive TFTS (Qd1(m,n), Qd2(m,n),Qd3(m,n)) are of a double gate structure to have a gate length of 10 μm,total channel length of 20 μm, and a channel width of 4 μm.

Supplying of current to the EL elements OLED(m,n) from the EL drive TFT(Qd2(m, n+1)) and the EL drive TFT (Qd3(m, n+2)) is made by extending p+type semiconductor layers, which constitute source electrodes and drainelectrodes of the respective EL drive TFTs, as they are and using thesame as wiring.

With such configuration, since formation of surplus contact throughholes is made unnecessary, surface efficiency is enhanced with theresult that numerical aperture is improved.

Take again notice of a pixel in row m and column n, the EL drive TFT(Qd2(m,n)) among the three EL drive TFTs (Qd1(m,n), Qd2(m,n), Qd3(m,n))is provided to drive an EL element OLED(m, n−1) of a pixel in row m andcolumn (n−1), and the EL drive TFT (Qd3(m,n)) is provided to drive an ELelement OLED(m, n−2) of a pixel in row m and column (n−2).

Also, the charge-storage capacitance Cst(m, n) is provided to hold anelectric potential of a gate electrode node of the EL drive TFT(Qd3(m,n)).

The EL elements are formed on ITO electrodes (anode electrodes of the ELelements) 13, which are connected to the EL connection wiring electrodes15 via contact through holes, through openings formed on organicinsulating films 23.

FIG. 3 is a circuit diagram showing an entire display unit includingequivalent networks and a driving circuit in a matrix display section ofthe display device according to the first embodiment.

As shown in FIG. 3, the matrix display section is composed of 600scanning signal wiring electrodes G1 to G600, 2400 picture signal wiringelectrodes D1R to D800R, D1G to D800G, and D1B to D800B, 2400 anodecurrent feeding wiring electrodes A1R to A800R, A1G to A800G, and A1B toA800B, and pixels provided in regions where these electrodes intersect.

The matrix display section is driven by a vertical scanning circuit VDRVand a picture signal circuit HDRV, and the anode current feeding wiringelectrodes arranged on the respective pixels are short-circuited outsidethe regions of pixels to be connected to an external electric powersource.

In the embodiment, since the EL drive TFTs are arranged in an associatedpixel, the next pixel on the right side and the further next pixel, tworows of dummy regions of pixels are provided outside a rightmost row ofpixels.

Further, two anode current feeding wiring electrodes (A02, A03) areprovided corresponding to the two rows of dummy regions of pixelsoutside the rightmost row of pixels.

Thus three anode current feeding wiring electrodes can also feed aspecified current to the rightmost row of pixels via three EL driveTFTs.

Here, three pixels, in which three EL drive TFTs are arranged as shownin FIG. 3, are ones arranged in the same direction as a laser scanningdirection of laser used when EL drive TFTs are manufactured.

In this manner, EL drive TFTs are scattered to be arranged in aplurality of pixels, and connected in parallel to drive one EL element,whereby current for the EL drive TFTs is averaged and so dispersion indrive current between pixels can be reduced to improve uniformity indisplay.

Also, since three anode current feeding wiring electrodes feed currentto one EL element via three EL drive TFTs at the same time, redundancyis provided for deficiency in display, which is caused by breaking ofanode current feeding wiring electrodes and failure in opening of ELdrive TFTs, thus enabling enhancing yield in manufacture.

Second Embodiment

FIG. 4 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a second embodiment of the invention, andFIG. 5 is a plan view showing a pixel arrangement in the display deviceaccording to the second embodiment of the invention.

As described above, with the self-luminescence display device accordingto the invention, EL elements of respective pixels are driven by threeEL drive TFTs provided on different pixel regions.

In the embodiment, respective EL drive TFTs are arranged in anassociated pixel, and the next pixels on the right and left sides.

FIG. 4 shows three regions of pixels surrounded by scanning signalwiring electrodes (Gm, G(m+1)), picture signal wiring electrodes (D(n−1)to D(n+2)), anode current feeding wiring electrodes (A(n−2) to A(n+1)),which constitute a part of the matrix.

A pixel in row m and column n is defined by a region, which issurrounded by scanning signal wiring electrodes (Gm, G(m+1)), a picturesignal wiring electrode Dn and an anode current feeding wiring electrodeAn, and there are formed in the pixel a switch TFT (Qs(m, n)), three ELdrive TFTs (Qd1(m,n), Qd2(m,n), Qd3(m,n)), and a charge-storagecapacitance Cst(m, n).

An anode electrode of an EL element OLED (m, n) is connected to a drainelectrode of the EL drive TFT (Qd2(m, n)) via an EL connection wiringelectrode 15.

An EL element OLED(m, n) belonging to a pixel in row m and column n isconnected not only to the EL drive TFT (Qd2(m, n)) in the pixel but alsoin parallel to an EL drive TFT (Qd3(m, n+1)) formed in an adjacent pixelin row m and column (n+1) and an EL drive TFT (Qd1(m, n−1)) formed in anpixel in row m and column (n−1) such that current is fed from threeanode current feeding wiring electrodes (A(n−1), An, A(n+1)).

All gate wiring electrodes 14 of the three parallel-connected EL driveTFTs are connected to a drain electrode of a switch TFT (Qs(m,n)) of apixel in row m and column n via an EL connection wiring electrode 12.

Also, a charge-storage capacitance Cst (m, n+1) is formed between gateelectrode nodes of the three EL drive TFTs and the anode current feedingwiring electrode A(n+1) to be able to keep voltage of the gate wiringelectrodes 14 for a predetermined period of time.

With the embodiment, gate length, channel length, and channel width areset so that current fed to the respective EL drive TFTs (Qd1, Qd2, Qd3)becomes substantially equal to a current fed by a single EL drive TFT.

In the embodiment, the respective EL drive TFTs (Qd1(m,n), Qd2(m,n),Qd3(m,n)) are of a double gate structure to have a gate length of 10 p,total channel length of 20 μm, and a channel width of 4 μm.

Supplying of current to the EL elements OLED(m,n) from the EL drive TFT(Qd1(m, n−1)) and the EL drive TFT (Qd3(m, n+1)) is made by extending p+type semiconductor layers, which constitute source electrodes and drainelectrodes of the respective EL drive TFTS, as they are and using thesame as wiring.

With such configuration, since formation of surplus contact throughholes is made unnecessary, surface efficiency is enhanced with theresult that numerical aperture is improved.

Taking again notice of a pixel in row m and column n, the EL drive TFT(Qd1(m,n)) among the three EL drive TFTs (Qd1(m,n), Qd2(m,n), Qd3(m,n))is provided to drive an EL element OLED(m, n+1) of a pixel in row m andcolumn (n+1), and the EL drive TFT (Qd3(m,n)) is provided to drive an ELelement OLED(m, n−1) of a pixel in row m and column (n−1).

Also, the charge-storage capacitance Cst(m, n) is provided to hold anelectric potential of a gate electrode node of the EL drive TFT(Qd3(m,n)).

The EL elements are formed on ITO electrodes (anode electrodes of the ELelements) 13, which are connected to the EL connection wiring electrodes15 via contact through holes, through openings formed on an organicinsulating film 23.

FIG. 6 is a circuit diagram of an entire display unit includingequivalent networks and a driving circuit in a matrix display section ofthe display device according to the second embodiment.

As shown in FIG. 6, the matrix display section is composed of 600scanning signal wiring electrodes G1 to G600, 2400 picture signal wiringelectrodes D1R to D800R, D1G to D800G, and D1B to D800B, 2400 anodecurrent feeding wiring electrodes A1R to A800R, A1G to A800G, and A1B toA800B, and pixels provided in regions where these electrodes intersect.

The matrix display section is driven by a vertical scanning circuit VDRVand a picture signal circuit HDRV, and the anode current feeding wiringelectrodes arranged on the respective pixels are short-circuited outsidethe regions of pixels to be connected to an external electric powersource.

In the embodiment, since the EL drive TFTs are arranged in an associatedpixel, and the next pixels on the right and left sides, two rows ofdummy regions of pixels are provided on both sides of leftmost andrightmost rows of pixels, respectively.

Further, two anode current feeding wiring electrodes (A00, A01) areprovided corresponding to the dummy pixels formed on the leftmost andrightmost rows of pixels.

Thus three anode current feeding wiring electrodes can also feed aspecified current to the leftmost and rightmost row of pixels via threeEL drive TFTs.

In this manner, EL drive TFTs are scattered to be arranged in aplurality of pixels, and connected in parallel to drive one EL element,whereby current for the EL drive TFTs is averaged and so dispersion indrive current between pixels can be reduced to improve uniformity indisplay.

Also, since three anode current feeding wiring electrodes feed currentto one EL element via three EL drive TFTs at the same time, redundancyis provided for deficiency in display, which is caused by breaking ofanode current feeding wiring electrodes and failure in opening of ELdrive TFTs, thus enabling enhancing yield in manufacture.

In the embodiment, the number of EL drive TFTs arranged in parallel isthree, and the EL drive TFTs are arranged in an associated pixel, andthe next pixels on the right and left sides.

In comparing with the embodiment described above, lengths of the currentfeeding wiring electrodes constituted by p+ type semiconductor layersfrom the EL drive TFT (Qd1(m,n−1)) and the EL drive TFT (Qd3(m,n+1)) tothe EL element OLED(m, n) can be made substantially the same.

Thereby, sums of wiring resistances of the EL drive TFT and the p+ typesemiconductor layers from the anode current feeding wiring electrodeA(n+1) and the anode current feeding wiring electrode A(n+1) to the ELelement OLED(m, n) can be made substantially the same.

Since the wiring resistance of the p+ type semiconductor layers isordinarily set to be lower than the ON resistance of the EL drive TFT,unbalance in the wiring resistance of the p+ type semiconductor layerscauses no significant problem but an error is caused when wiring lengthis increased.

An error due to unbalance in the wiring resistance of the p+ typesemiconductor layers can be minimized by arranging EL drive TFTs in thenext pixels on both sides as in the embodiment.

FIG. 7 is a cross sectional view showing a cross-sectional structure cutalong the line X-X′ shown in FIG. 5.

As shown in FIG. 7, a buffer Si₃N₄ film 200 having a thickness of 50 nmand a buffer SiO₂ film 2 having a thickness of 100 nm are formed on anon-alkali glass substrate 1 having a thickness of 0.5 mm and a straintemperature of about 670° c.

These buffer insulating films (200, 2) serve to prevent dispersion ofimpurities, such as Na or the like, from the glass substrate 1.

Formed on the buffer SiO₂ film 2 is a polycrystal Si (referred below toas poly-Si) film 30 having a thickness of 50 nm and corresponding to thecharge-storage capacitance Cst(m, n), and formed on the poly-Si film 30through a gate insulating film 20 formed from SiO₂ are gate wiringelectrodes 14 of the EL drive TFTs composed of Mo.

Anode current feeding wiring electrodes An are formed on the gate wiringelectrodes 14 of the EL drive TFTs through an interlayer insulating film21 composed of SiO₂, and are of a three-layered electrode structurecomposed of Mo (110 a), Al (110 b), and Mo (110 c).

Here, the gate wiring electrode 14 of the EL drive TFT (Qd3(m, n)) shownin FIG. 7 is shown as its portion being extended below the anode currentfeeding wiring electrode An such that the gate wiring electrode 14 ofthe EL drive TFT (Qd3(m, n)) overlaps the anode current feeding wiringelectrode An as shown in FIG. 5.

Also, the poly-Si film 30 shown in FIG. 7 is formed to overlap the anodecurrent feeding wiring electrode An as shown in FIG. 5, and the poly-Sifilm 30 is electrically connected to the anode current feeding wiringelectrode An via a contact hole (CHO in FIG. 5).

Accordingly, in the embodiment, the charge-storage capacitance Cst(m, n)is defined by a capacitative element formed by the interlayer insulatingfilm 21 between the anode current feeding wiring electrode An and thegate wiring electrode 14, and a capacitative element formed by a gateinsulating film 20 between the gate wiring electrode 14 and the poly-Sifilm 30.

In this manner, pixels are improved in numerical aperture by forming thecharge-storage capacitance Cst(m, n) below the anode current feedingwiring electrode An.

Also, picture signal wiring electrodes (Dn, D(n+1)) are also formed onthe same layer as the anode current feeding wiring electrode An, and thepicture signal wiring electrodes (Dn, D(n+1)) are of a three-layeredelectrode structure composed of Mo (11 a), Al (11 b), and Mo (11 c).

All these constituents are covered by a protective insulating film 22having a film thickness of 200 nm and composed of Si₃N₄, on which filmis formed an anode electrode 13 composed of an indium-tin oxide (ITO).

Further, an organic insulating film 23 having a film thickness of 2 μmand containing polyimide as its main component is formed on the anodeelectrode 13, and the organic insulating film 23 is providedsubstantially centrally of the anode electrode 13 with an opening.

Formed on the anode electrode 13 and the organic insulating film 23 isan electron hole transport layer 300 having a film thickness of 150 nmand composed of triphenyldiamine (TPD), and formed on the layer are ared EL luminescent layer 301R composed of a tris (8-hydroxyquinoline)aluminum (Alq3) having a film thickness of 30 nm and doped with DCJTBand rubrene, and an electron transport layer (not shown) having a filmthickness of 30 nm and composed of Alq3.

Formed above the electron transport layer through LiF having a filmthickness of 0.8 nm is a cathode electrode 302 having a film thicknessof 150 nm.

Electron holes injected from the anode electrode 13 and electronsinjected from the cathode electrode 302 make radiational reunion in thered EL luminescent layer 301R to cause emission.

Light generated is emitted toward the glass substrate 1.

Arranged in adjacent pixels are blue dots and green dots, on which ablue EL luminescent layer 301B and a green EL luminescent layer 301G areformed in place of a red EL luminescent layer.

The blue EL luminescent layer 301B is DPVBi doped with BCzVBi having afilm thickness of 15 nm, and the green EL luminescent layer 301G is Alq3doped with coumarin 540 having a film thickness of 30 nm.

FIG. 8 is a cross sectional view showing a cross-sectional structure cutalong the cut line Y-Y′ shown in FIG. 5, and FIG. 9 is a cross sectionalview showing a cross-sectional structure cut along the cut line Z-Z′shown in FIG. 5.

As described above, the buffer Si₃N₄ film 200 having a thickness of 50nm and the buffer SiO₂ film 2 having a thickness of 100 nm are formed onthe non-alkali glass substrate 1, the poly-Si film 30 having a thicknessof 50 nm and corresponding to the switch TFT (Qs(m,n)) and the EL driveTFT (Qd2(m, n)) is formed on the films, and the scanning signal wiringelectrodes Gm and the gate wiring electrodes 14 of the EL drive TFTs areformed on the poly-Si film 30 through the gate insulating film 20 formedfrom SiO₂.

Here, the scanning signal wiring electrodes Gm are formed from Mo.

The switch TFT (Qs(m,n)) is composed of a N type TFT, the picture signalwiring electrode Dn is connected to a source electrode of the switch TFTthrough a contact hole opened to the interlayer insulating film 21, andthe connection wiring electrode 12 is connected to a drain electrode ofthe switch TFT.

As described above, the picture signal wiring electrode Dn is of athree-layered electrode structure composed of Mo (11 a), Al (11 b), andMo (11 c), and likewise the connection wiring electrodes 12 are of athree-layered electrode structure composed of Mo (12 a), Al (12 b), andMo (12 c).

The other of the connection wiring electrodes 12 is also connected tothe gate wiring electrodes 14 of the EL drive TFTs via through holesformed in the interlayer insulating film 21, so that a signal voltage ofthe picture signal wiring electrode Dn is applied to the gate wiringelectrode 14 of the EL drive TFT via the switch TFT (Qs(m,n)).

Meanwhile, the EL drive TFT (Qd2(m, n)) is composed of a Ptype TFT, to asource electrode of which the anode current feeding wiring electrode Anis connected via a contact hole opened to the interlayer insulating film21.

As described above, the anode current feeding wiring electrode An is ofa three-layered electrode structure composed of Mo (110 a), Al (110 b),and Mo (110 c).

A drain electrode of the EL drive TFT (Qd2(m, n)) is made common todrain electrodes of the EL drive TFT (Qd1(m,n−1)) and the EL drive TFT(Qd3(m,n+1)), which are adjacent to the EL drive TFT (Qd2(m, n)), to beconnected to the EL connection wiring electrode 15.

Here, the EL connection wiring electrodes 15 are of a three-layeredelectrode structure composed of Mo (15 a), Al (15 b), and Mo (15 c).

Also, the anode electrodes 13 are connected to the EL connection wiringelectrodes 15 via through holes formed in the protective insulating film22 having a film thickness of 200 nm and composed of Si₃N₄.

Organic LEDs having the above layered structure are formed above theanode electrodes 13.

Third Embodiment

FIG. 10 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a third embodiment of the invention, andFIG. 11 is a plan view showing a pixel arrangement in the display deviceaccording to the third embodiment of the invention.

With the self-luminescence display device according to the embodiment,an EL element OLED(m, n) in row m and column n is driven by fiveparallel EL drive TFTs formed in total five regions of pixels in row mand column (n−2), row m and column (n−1), row m and column (n+1), androw m and column (n+2) as well as in row m and column n.

Since the number in parallel is five, such averaging greatly contributesto improvement in uniformity, which makes it possible to obtain anenhanced uniform display characteristics.

Fourth Embodiment

FIG. 12 is a circuit diagram showing equivalent networks for pixels in adisplay device according to a fourth embodiment of the invention, andFIG. 13 is a plan view showing a pixel arrangement in the display deviceaccording to the fourth embodiment of the invention.

With the self-luminescence display device according to the embodiment,an EL element OLED(m, n) in row m and column n is driven by six parallelEL drive TFTs formed in total six regions of pixels in row m and column(n+1), row m and column (n+2), row m and column (n+3), row m and column(n+4), and row m and column (n+5) as well as in row m and column n.

Since the number in parallel is six, such averaging greatly contributesto improvement in uniformity, which makes it possible to obtain anenhanced uniform display characteristics.

Also, the embodiment adopts a configuration, in which light emitted fromthe EL elements is taken not from a side of the substrate but a side ofa front surface.

When the number of TFTs in pixels is increased as in the embodiment, itbecomes difficult to ensure an area of those EL elements, whichcontribute to emission of light.

In such case, that configuration, in which light is taken from the sideof a front surface, is advantageous.

FIG. 14 is a cross sectional view showing a cross-sectional structurecut along the line X-X′ shown in FIG. 13. As shown in FIG. 14, a bufferSi₃N₄ film 200 having a thickness of 50 nm and a buffer SiO₂ film 2having a thickness of 100 nm are formed on a non-alkali glass substrate1 having a thickness of 0.5 mm and a strain temperature of about 670° C.

Formed on the buffer SiO₂ film 2 is a polycrystal Si film 30 having athickness of 50 nm and corresponding to the charge-storage capacitanceCst(m, n), and formed on the poly-Si film 30 through a gate insulatingfilm 20 formed from SiO₂ are gate wiring electrodes 14 of the EL driveTFTs composed of Mo.

The gate wiring electrode 14 of the EL drive TFT (Qd3(m, n)) shown inFIG. 14 is shown as its portion being extended below an associated pixelas shown in FIG. 13, and the poly-Si film 30 shown in FIG. 14 iselectrically connected to the anode current feeding wiring electrode Anthrough the contact hole as shown in FIG. 13.

The anode current feeding wiring electrode An is formed above the gatewiring electrode 14 of the EL drive TFT with an interlayer insulatingfilm 21 formed from SiO₂ therebetween. The anode current feeding wiringelectrode An is of a three-layered electrode structure composed of Mo(110 a), Al (10 b), and Mo (110 c).

Also, a picture signal wiring electrode Dn and a reflective film 17 arealso formed on the same layer as the anode current feeding wiringelectrode An.

The picture signal wiring electrode Dn is of a three-layered electrodestructure composed of Mo (11 a), Al (11 b), and Mo (11 c), and thereflective film 17 is also of a three-layered electrode structurecomposed of Mo/Al/Mo.

The reflective film 17 is connected to an anode electrode 13 viaopenings (CH1, Cf2 in FIG. 13) formed in a protective insulating film 22having a film thickness of 200 nm and composed of Si₃N₄.

The reflective film 17 is formed in a region in, for example, a pixel inrow m and column n, except for that region, in which a switch TFT and anEL drive TFT (Qd1(m,n)) are formed.

The reflective film 17 serves to reflect light emitted from an ELelement to a front surface and constitutes a part of the charge-storagecapacitance Cst(m, n) between it and the poly-Si film 30 when the ELdrive TFT (Qd3(m, n)) is ON.

Accordingly, in the embodiment, the charge-storage capacitance Cst(m, n)is defined by a capacitative element formed by the gate insulating film20 between the gate wiring electrode 14 and the poly-Si film 30, and acapacitative element formed by an interlayer insulating film 21 betweenthe reflective film 17 and the poly-Si film 30.

All these constituents are covered by a protective insulating film 22having a film thickness of 200 nm and formed from Si₃N₄, on which filmis formed an anode electrode 13 composed of an indium-tin oxide (ITO).

Further, an organic insulating film 23 having a film thickness of 2 μmand containing polyimide as its main component is formed on the anodeelectrode 13, and the organic insulating film 23 is providedsubstantially centrally of the anode electrode 13 with an opening.

Formed on the anode electrode 13 and the organic insulating film 23 isan electron hole transport layer 300 having a film thickness of 150 nmand composed of triphenyldiamine (TPD), and formed on the layer are ared EL luminescent layer 301R and composed of a tris(8-hydroxyquinoline) aluminum (Alq3) having a film thickness of 30 nmand doped with DCJTB and rubrene, and an electron hole transport layer(not shown) having a film thickness of 30 nm and composed of Alq3.

Formed above the electron hole transport layer through LiF having a filmthickness of 0.8 nm are 2-9-dimethyl-4, 7diphenyl-1,10-phenanthroline(BCP) having a film thickness of 7 nm and ITO having a film thickness of77 nm to constitute a transparent cathode electrode 302.

Electron holes injected from the anode electrode 13 and electronsinjected from the cathode electrode 302 make radiational reunion in thered EL luminescent layer 301R to cause emission.

Light generated is emitted toward the transparent cathode electrode.

Arranged in adjacent pixels are blue dots and green dots, on which ablue EL luminescent layer 301B and a green EL luminescent layer 301G areformed in place of a red EL luminescent layer.

The blue EL luminescent layer is DPVBi doped with BCzVBi having a filmthickness of 15 nm, and the green EL luminescent layer is Alq3 dopedwith coumarin 540 having a film thickness of 30 nm.

FIG. 15 is a graph indicating the relationship between the number N ofparallel EL drive TFTs and dispersion (MAX−MIN)/(MAX+MIN) in luminanceamong pixels.

As seen from the graph in FIG. 15, dispersion in luminance in the caseof N=3 can be reduced to about a half of that in the case of N=1.

Theoretically, it is presumed that with respect to the parallel numberN, the degree of dispersion is decreased inversely proportional to √N.

According to the graph in FIG. 15, a dispersion decreasing effect asappropriately presumed theoretically is obtained.

Fifth Embodiment

An entire configuration of the display device according to the inventionin a fifth embodiment of the invention will be described below withreference to FIGS. 16 to 18.

Formed on the glass substrate 1 are an active matrix AMX constituted byTFTs, a vertical scanning circuit VDRV and a picture signal circuitHDRV.

The cathode electrode 302 of the EL element OLED is connected to awiring 401 taken out and formed on the glass substrate 1 through acontact hole in a contact area 400 and then to an external connectionterminal PAD.

Also, all anode current feeding wiring electrodes A provided inrespective columns in pixels are connected outside pixel regions to theexternal connection terminal PAD through a taken-out electrode 402.

The embodiment has a feature in that the contact area 400 is arrangedbetween the active matrix AMX and the external connection terminal PADand the picture signal circuit HDRV is disposed on an opposite side ofthe active matrix AMX to the external connection terminal PAD.

With such arrangement, the taken-out wiring 401 extending from theexternal connection terminal PAD to the contact area 400 can be madeshort, so that voltage drop and power consumption caused by resistanceof the taken-out wiring can be minimized.

Since current from the EL elements OLED in all pixels flows through thetaken-out wiring of the cathode electrode 302, reduction in resistanceof the taken-out wiring is important.

Meanwhile, since current flowing through a power source wiring andground wiring to the picture signal circuit HDRV is small as comparedwith current flowing through the EL elements OLED, no significantproblem is caused even when such wirings are lengthened more or less.

FIG. 17 is an exploded, perspective view showing the entire displaydevice shown in FIG. 16.

A seal glass 600 is mounted through a seal SHL on the glass substrate 1,on which the cathode electrode 302 of the EL elements OLED is formed,whereby the EL elements OLED are not exposed to outside air.

Used for the seal SHL is an ultraviolet hardening-type resin, in whichfiber glass having a diameter of 10 μm is dispersed.

The seal glass and the glass substrate 1 substantially correspond toeach other in external shape at three sides except a side, from whichthe external connection terminal PAD is taken out, so that the entirepanel is made minimum in external dimension.

FIG. 18 is a cross sectional view showing a cross-sectional structure ofthe display device shown in FIG. 16.

A chemical adsorbent 602 for absorbing moisture entering from outsideand a gas emitted from a material, which forms the EL elements OLED, isheld on projections provided in the seal glass 600 by means of a tape601.

Calcium oxide (CaO) was used as the chemical adsorbent.

Also, a dry N2 gas, from which moisture is removed up to the dew-pointof −78° C., is sealed in a cavity in the seal glass 600.

Sixth Embodiment

A manufacturing process, according to a sixth embodiment of theinvention, for an active matrix substrate in the display deviceaccording to the second embodiment will be described below withreference to FIGS. 19 to 27.

First, the plasma CVD method making use of a mixture gas of SiH₄, NH₃and N₂ is used to form a Si₃N₄ film 200 having a thickness of 50 nmafter a non-alkali glass substrate 1 having a thickness of 0.5 mm, alength of 750 mm and a width of 950 mm and a strain temperature of about670° C. is cleaned.

Subsequently, the plasma CVD method making use of a mixture gas oftetraethoxysilane and O₂ is used to form a SiO₂ film 2 having athickness of 120 nm.

In addition, both Si₃N₄ and SiO₂ are formed at temperature of 400° C.

Then a substantially intrinsic hydro-amorphous silicon film 35 having athickness of 50 nm is formed on the SiO₂ film 2 by the plasma CVD methodmaking use of a mixture gas of SiH₄ and Ar.

A deposition temperature was 400° C. and an amount of hydrogen was about5 atomic % immediately after deposition.

Subsequently, the substrate is annealed at 450° C. for about 30 minuteswhereby hydrogen in the hydro-amorphous silicon film 35 is caused to bereleased.

Subsequently, the plasma CVD method making use of a mixture gas oftetraethoxysilane and O₂ is used to form a SiO₂ film 201 having athickness of 100 nm, and then boron (B+) is implanted in a dose 5×10¹²(atoms/cm²) at acceleration voltage of 40 KeV by ion-implantation.

Boron serves to adjust a threshold voltage of TFT (see FIG. 19).

Subsequently, the SiO₂ film 201 is removed by a buffer hydrofluoricacid, and pulse excimer laser of a wavelength of 308 nm processed in theform of stripe having a short side of 0.3 mm and a long side of 300 mmis irradiated on the amorphous silicon film 35 at a fluence of 450mJ/cm² while moving at 10 μm in a direction along the short side,whereby the amorphous silicon film 35 is melted and recrystallized toprovide a P type polycrystal silicon film 30 (see FIG. 20).

At this time, dispersion in the TFT characteristics caused by dispersionin crystal quality of the polycrystal silicon in a scanning direction oflaser beam generally tends to become greater than dispersion in adirection perpendicular to the scanning direction of laser beam.

Therefore, a great effect is obtained by arranging a plurality of ELdrive TFTs in parallel in the scanning direction of laser beam.

The scanning direction of laser beam shown by arrows in FIG. 3 or 6indicates this, and the plurality of EL drive TFTs are arrangedsubstantially in parallel in the scanning direction of laser beam.

The same is with the embodiment shown in FIGS. 10 and 12.

Subsequently, the reactive ion etching method making use of CF₄ is usedto process the P type polycrystal silicon film 30 in a predeterminedform to obtain TFTs and a wiring pattern (P type polycrystal siliconfilm 30) except the TFTs.

Subsequently, the plasma CVD method making use of a mixture gas oftetraethoxysilane and O₂ is used to form SiO₂ having a thickness of 100nm to form a gate insulating film 20.

Subsequently, after the sputtering method is used to form a Mo filmhaving a thickness of 200 nm, an ordinary photolithography method isused to form a predetermined resist pattern PR on the Mo film, and thereactive ion etching method making use of CF₄ is used to process the Mofilm in a predetermined form to obtain gate electrodes 10N for N typeTFTs.

Subsequently, while the resist pattern PR used in etching is left,phosphorus (P) ions are implanted in a dose 10¹⁵ (atoms/cm²) atacceleration voltage of 60 KeV by ion-implantation to form regions ofsource electrodes and drain electrodes for N type TFTs (see rightwardand central portions in FIG. 21).

At this time, all the elements are protected by patterns of the Mo filmand the photoresist film PR to prevent phosphorus ions from beingimplanted into the P type TFTs (see a leftward portion in FIG. 21).

Subsequently, while the resist pattern is left, the substrate isprocessed by a mixed acid and the Mo electrodes thus processed aresubjected to side etching whereby the pattern is slimmed and the resistis removed, after which P ions are implanted in a dose 2×10¹³(atoms/cm²) at acceleration voltage of 65 KeV by ion-implantation toform LDD regions for N type TFTs.

The LDD regions are controlled in length by a side etching time with themixed acid (see FIG. 22).

Subsequently, a predetermined resist pattern is formed on the Mo film,and the reactive ion etching method making use of CF₄ is used to obtaingate electrodes 10P for P type TFTs and a wiring pattern (gate wiringelectrode 14) except the TFTs.

Using the gate electrodes 10P for P type TFTs as a mask, boron ions areimplanted in a dose 10¹⁵ (atoms/cm²) at acceleration voltage of 40 KeVby ion-implantation to form regions of source electrodes and drainelectrodes for P type TFTs.

At this time, all N type TFTs are protected by the photoresist patternPR to be protected from the etching gas and prevent boron ions frombeing implanted thereinto (see FIG. 23).

After the photoresist is removed, ultraviolet light from an excimer lampor metal halide lamp is irradiated to activate impurities implanted bythe rapid thermal anneal (RTA) method (see FIG. 24).

Subsequently, the plasma CVD method making use of a mixture gas oftetraethoxysilane and oxygen is used to form SiO₂ having a filmthickness of 500 nm to form an interlayer insulating film 21.

After a predetermined resist pattern is formed, the wet etching methodmaking use of a mixed acid is used to form contact through holes in theinterlayer insulating film 21.

Subsequently, after the sputtering method is used to sequentiallylaminate Mo film of 50 nm, an Al—Nd alloy of 500 nm and Mo of 50 nm, apredetermined resist pattern is formed, and then the reactive ionetching method making use of a mixed gas of BCl₃ and Cl₂ performsetching collectively to fabricate picture signal wiring electrodes D,anode current feeding wiring electrodes A, connection wiring electrodes12 and EL connection wiring electrodes 15 (see FIG. 25).

Subsequently, the plasma CVD method making use of a mixture gas of SiH₄,NH₃ and N₂ is used to form a Si₃N₄ film having a thickness of 400 nm tomake the same a protective insulating film 22.

After a predetermined photoresist pattern is formed, the dry etchingmethod making use of SF₆ is used to form contact through holes in theprotective insulating film 22.

Succeedingly, the sputtering method is used to form an ITO film of 70 nmand the wet etching method making use of a mixed acid is used to processthe film in a predetermined shape to form anode electrode 13 for ELelements OLED (see FIG. 26).

Finally, the spin coating method is used to coat a photosensitivepolyimide resin in a film thickness of about 3.5 μm, and a predeterminedmask is used to perform exposure and development to remove the polyimideresin in those portions of the anode electrode, on which EL elementsOLED are formed, thereafter performing baking the polyimide resin for 30minutes at 350° C. to form an organic insulating film 23 having a filmthickness of 2.3 μm (see FIG. 27).

The organic insulating film 23 is formed to cover ends of the anodeelectrode 13 to prevent the EL elements OLED from being broken by fieldconcentration at ends of the ITO electrodes when a very thin organicfilm forming the EL elements OLED is formed on the anode electrode.

A process of forming EL elements on an active matrix substratefabricated by the above processes will be described below.

The active matrix substrate is set in a vacuum deposition device, andfirst introduced into a preheating chamber to be baked under vacuum forone hour at 200° C., whereby moisture adsorbing to surfaces of thesubstrate and moisture contained in the organic insulating film 23 areremoved.

Subsequently, ultraviolet light is irradiated at the intensity of 60mW/cm² for 60 seconds in an atmosphere containing oxygen to removeorganic substances on the surfaces of the anode electrode.

Subsequently, the active matrix substrate is moved into a pretreatmentchamber to be subjected to O₂ plasma processing whereby the surfaces ofthe anode electrode are adjusted in work function.

The processing condition involves 60 seconds at the RF power of 200 W.

This processing adjusts the work function of ITOs being the anodeelectrode 13 at 5.1 to 5.2 eV, and decreases a barrier level whenelectrons are injected into an electron hole transport material, wherebyan efficiency of injection can be enhanced.

Subsequently, the active matrix substrate is moved into a firstdeposition chamber to be subjected to mask deposition with a mask, inwhich an electron hole transport layer is formed on an entire displaysurface.

Triphenyldiamine (TPD) is used for a material of the electron holetransport layer.

Besides this, for example, α-NPD can be used.

The electron hole transport layer has a film thickness of 150 nm.

Subsequently, the active matrix substrate is moved into a seconddeposition chamber to be subjected to mask deposition of luminescentmaterials for respective RGBs.

In deposition of different luminescent materials, predeterminedmaterials are formed in dot positions of respective RGBs by first makingregister between dots representative of blue color and openings in adeposition mask, forming a blue material, shifting the deposition mask apitch of one dot within the deposition chamber, making deposition of agreen material, and further moving the deposition mask similarly to makedeposition of a red material.

Subsequently, the active matrix substrate is moved into a thirddeposition chamber to form a cathode electrode 302.

In order to enhance an efficiency of electron injection for the organiclayer, the cathode electrode 302 is formed such that after LiF is formedto have a film thickness of around 0.8 nm, Al is formed to have athickness of 150 nm.

Subsequently, the active matrix substrate is moved into a seal chamber,a seal glass having been beforehand baked like the active matrixsubstrate for dehydration is bonded to the active matrix substrate withan ultraviolet hardening-type resin therebetween, and ultraviolet lightis irradiated on a back surface of the active matrix substrate to curethe resin. At this time, a chemical adsorbent is inserted into an airgap in the seal glass.

All the preceding steps after setting of the active matrix substratemust be effected in a state, in which the active matrix substrate is notexposed to the atmospheric air.

Finally, the active matrix substrate, to which the seal glass is bonded,is taken out to be cut into a predetermined size, and driver LSIs areloaded on the substrate to finish a panel.

While the invention having been thought of by the inventors of thisapplication has been concretely described on the basis of theembodiments, it is not limited to the embodiments but can be of coursemodified within a scope not departing from the gist thereof.

Effects obtained by typical configurations of the invention disclosed inthis application are simply described below.

-   (1) It is possible in a self-luminescence display device according    to the invention to obtain a uniform display screen free of    unevenness.-   (2) It is possible in a self-luminescence display device according    to the invention to reduce voltage drop and power consumption caused    by resistance of the taken-out wiring of the cathode electrodes.

1. An EL display device comprising a plurality of EL pixels, each pixelbeing comprised of an anode electrode, an electroluminescent layer, acathode electrode, a drive TFT, a scanning signal wiring, a picturesignal wiring, and an anode current feeding wiring, wherein the anodeelectrode of one of the EL pixels is connected to the drive TFT of saidone pixel formed under said one pixel, and to the drive TFT formed underanother one of said pixels, each pixel further comprising a switch TFTincluding a gate electrode connected to the scanning signal wiring ofthe pixel, a source electrode connected to the picture signal wiring ofthe pixel, and a drain electrode connected to gate electrodes of thedrive TFT of the pixel and to drive TFT of another pixel, wherein asource electrode of the drive TFT of the one pixel is connected to thecorresponding anode current feeding wiring which belongs to the onepixel, and a source electrode of the drive TFT of said another pixel isconnected to the corresponding anode current feeding wiring whichbelongs to the another pixel.
 2. The EL display device according toclaim 1, wherein both a drain electrode of the drive TFT of the onepixel and a drain electrode of the drive TFT of the another pixel areconnected to the anode electrode of the said one pixel.
 3. The ELdisplay device according to claim 1, wherein the drive TFT of said onepixel and the drive TFT of said another pixel are arranged at differentdistances from a corresponding one of the scanning signal wirings in aplan view.
 4. An EL display device comprising a first EL pixel and asecond EL pixel, wherein said first EL pixel and said second EL pixelare each comprised of an anode electrode, an electroluminescent layer, acathode electrode, a drive TFT, a scanning signal wiring, a picturesignal wiring, and an anode current feeding wiring, wherein an anodeelectrode of the first EL pixel is connected and driven by a first driveTFT formed under the first EL pixel and by a second drive TFT formedunder the second EL pixel, and wherein a switch TFT of the first ELpixel includes a gate electrode connected to the scanning signal wiring,a source electrode connected to the picture signal wiring, and a drainelectrode connected to a gate electrode of the first drive TFT and to agate electrode of the second drive TFT, wherein a source electrode ofthe drive TFT of the one pixel is connected to the corresponding anodecurrent feeding wiring which belongs to the one pixel, and a sourceelectrode of the drive TFT of said another pixel is connected to thecorresponding anode current feeding wiring which belongs to the anotherpixel.
 5. The EL display device according to claim 4, wherein both adrain electrode of the first drive TFT and a drain electrode of thesecond drive TFT are connected to the anode electrode of the first ELpixel.
 6. The EL display device according to claim 5, wherein the firstdrive TFT and the second drive TFT are arranged at different distancesfrom one of the scanning signal wirings in a plan view.
 7. The ELdisplay device according to claim 4, further comprising a third EL pixeland a third drive TFT, wherein the third drive TFT is arranged under thethird EL pixel and a gate electrode of the third drive TFT is connectedto the drain electrode of the switch TFT, a source electrode of thethird drive TFT is connected to the anode current feeding wiring whichbelongs to the third EL pixel, and a drain electrode of the third driveTFT is connected to the another electrode of the first EL pixel.
 8. TheEL display device according to claim 7, wherein the first drive TFT, thesecond drive TFT and the third drive TFT are arranged at differentdistances from one of the scanning signal wirings in a plan view.